1. Field of the Invention
This invention relates to the field of mountings for rotating shafts, and in particular to an inexpensive self-centering mounting for a water lubricated pump shaft rotatable within a tube.
2. Prior Art
It is known to employ a rubber sleeve or similar type of resilient bushing as a friction reducing element supporting a shaft and adapted to be lubricated by water. Rubber is, of course, a resilient waterproof material. Water between the rubber bearing and the shaft lubricates the rubber bearing. This effect can be maximized by carrying water to the area of the bearing by ridges or grooves formed in the rubber bearing, bushing or the like. Such bearing and bushings are employed in propeller shaft mounts for boats, in water pumps and in other similar applications. Reference can be made, for example, to U.S. Pat. No. 3,515,449.
In connection with substantially-elongated rotatable shafts to be substantially torqued and/or operated at high RPM., it is necessary either to provide a very massive and/or large diameter shaft, or to support the shaft at a plurality of axially spaced locations along its length. It has been proposed to support a shaft within an annular supporting ring or tube using a resilient mounting in which spring-like material is disposed in a circle or configured as a spiral wrapping bearing radially inwardly on the shaft, and tending resiliently to keep the shaft in place at the center of the ring or tube. The ring or tube is then rigidly fixed in place, e.g., to the boat hull or pump housing. Examples can be found in U.S. Pat. Nos. 4,526,483 and 4,549,821. Such devices can be characterized as mounting the shaft by means of an axially symmetrical, inwardly directed spring. The difficulty with such a spring mounting is that spring force is proportional to displacement. Therefore, when the shaft is correctly centrally positioned in the mounting, the minimum amount of spring pressure is exerted on the shaft for keeping the shaft in position. Oscillations and imbalances can thereby develop and increase with resonant effects. While it may be possible to improve this characteristic by employing a strong spring pressure according to devices of this type, the fact remains that the minimum available pressure is exerted on the shaft when the shaft is centrally positioned, allowing the maximum freedom for initiation of oscillation of the shaft at precisely the area in which the shaft is intended to be maintained in place and to most frequently reside.
U.S. Pat. No. 4,177,022 discloses an attempt to hold a rubber bushing for a pump at a central position within a tube, by means of a wire holder or "spider". An inner loop encloses the rubber bushing and an outer loop bears outwardly on the pump casing, shaped as a tube. A wire web connecting the inner and outer loops is all that is provided to minimize displacement. In such a device, the resistance against displacement of the shaft is directional, i.e., is strongest along the radial line of extension of the wire between the inner and outer loops, and weakest at angles perpendicular thereto. If such a wire is disposed in a spiral, very little pressure is exerted to keep the shaft centered.
In the event a very thin driven shaft, for example between a driving motor and a propeller or the like, is insufficiently supported, imbalances in the weight of the shaft and driving force can cause the shaft to bow outwardly between the points at which the shaft is supported. The force causing such bowing is dependent upon load imbalances, torque resonance and angular velocity. For higher speed operation, supports must be spaced closely and/or the shaft must be made thick to reduce imbalances tending to bow or whip the shaft. Multiplying the number of supports and increasing the weight of the mechanical parts increase the expense of pumps and other driven machines. Therefore, there is a need to support a shaft in a manner that will facilitate use of a very light-weight shaft, with a minimum number of axially spaced supports, and a high relative force exerted holding the shaft against displacement even while in its central, properly-fixed position.
The present invention approaches the problem by producing a resilient mounting which is characterized by plate-like resilient supports opposed to produce substantial pressure on the shaft at angularly spaced points around the shaft mounting. This is accomplished preferably by means of springy stainless steel plates which are disposed within a tube, for example a liquid-carrying tube of a pump, and bowed inwardly against the shaft, whereby even in the properly-centered position, substantial pressure is exerted on the shaft by the plate-like mounting webs. These webs are relatively simple and uncomplicated, thereby decreasing expense. The webs can be elongated along the axis of the shaft, for example one or several inches in width, the shaft being thereby supported along such elongation, and the webs spreading their force and improving the extent of stabilization of the overall shaft. The mounts themselves are easily installed, and are inexpensive yet effective.